1. Related Technical Fields
Related technical fields include a vehicle location recognition device for use in a navigation device or the like.
2. Description of the Related Art
Known navigation devices perform operations such as the display of vehicle location and guidance along a route to the destination by using road map data for actual roads. Such road map data is usually in the form of digital road network data for a combination of nodes and links. “Node” generally refers to a coordinate point representing an intersection or a curve in a road or the like. The respective nodes are connected by the links. Such connections of a plurality of links form a road network. Link information representing the attributes of the link is provided for each link. The link attributes include, for example, the link number, the coordinates of a start point node and an end point node of the link, the length (distance) of the link, the road type or class, the road width, the traffic regulations, and so forth.
The navigation apparatus obtains the location of its host vehicle in accordance with a method such as satellite navigation using a GPS (Global Positioning System) or autonomous navigation using an in-vehicle sensor and, based on the obtained information, locates the vehicle on a road map. At a narrow-angle branch point at which a road divides into branch roads at a relatively small angle, however, the vehicle may be located on a road different from the road where the vehicle is actually located due to an error in the satellite or autonomous navigation. When the navigation apparatus superimposes the vehicle location on a road map display, if the displayed vehicle location is different from the actual vehicle location, the driver may become confused.
To improve the accuracy of recognition of vehicle location at a narrow-angle branch point, Japanese Unexamined Patent Application Publication (Kokai)No. 2005-292082 (e.g., in paragraphs [0002] to [0012]) describes a technique for increasing the accuracy of location determination by a receiver of satellite signals. According to the disclosed technique, a high-accuracy location measurement unit would be used to reduce erroneous mapping due to error in the conventional measurement. Further, Japanese Unexamined Patent Application Publication No. 2006-017644 (e.g., in paragraphs [0016] to [0024]) describes a navigation apparatus which determines which one of branch roads is being traveled by the vehicle, on the basis of a threshold for the vehicle speed based on the speed limit of the branch road and signals from a direction indicator used to indicate an intention to change lanes.
A navigation apparatus conventionally provides other functions including guidance along the route to the destination and the provision of information relevant to the route. Information relevant to the route might include, for example, guidance to a rest area, guidance to a roadside station or a service area and guidance to the next interchange. If the destination has been input to the navigation apparatus, a route for the vehicle to the destination is determined by search. However, if a destination has not been input, a virtual destination area may be calculated in accordance with the direction of travel of the vehicle, and information for a route to the calculated virtual destination. In determining such a virtual destination area, if the route includes a branch point, it is difficult to predict for setting the virtual destination area ahead of the branch point. Japanese Unexamined Patent Application Publication (Kokai)No. 2006-284254 (e.g., paragraphs [0002] to [0007] and paragraphs [0043] to [0059]) proposes a course prediction method for predicting and presenting a course leaving the branch point, on the basis of the past history of the driver at the branch point. Based on the predicted course from the branch point, the virtual destination area is predicted, and information for guidance along the route to the predicted destination area is provided.
If the accuracy of the location determination at a narrow-angle branch point is increased as described in the aforementioned Japanese Kokai 2005-292082, erroneous mapping can be substantially reduced. However, the disclosed high-accuracy location measurement unit is expensive, and thus substantially increases the cost of the entire navigation apparatus. If the technique described in Japanese Kokai 2006-017644 is used, the accuracy of identifying the road, i.e., the link at the narrow-angle branch point, may be improved; however, the vehicle speed and the state of direction indicator, for example, in combination, will produce a variety of results, depending on the location of the branch point, the operation by the driver, and so forth. Further, the technique uses vehicle information different from that based on receipt of satellite signals or autonomous navigation and the operation of the navigation apparatus is thereby complicated.
The course prediction method described in Kokai 2006-284254 is a technique which predicts, as a probability based on past history, the route leaving the branch point before the vehicle reaches the branch point. That is, without tracing a travel route beyond the branch point, this course prediction method predicts the road leaving the branch point, i.e., the link to be actually traveled by the vehicle immediately beyond the branch point. Thus, there is no map matching with the predicted route beyond the branch point. Further, the necessity of such map matching is not recognized. Thus, the issue of map matching at a narrow-angle branch point still remains unresolved.